One of the players, Joe Campbell, said even though Microsoft has flipped the switch, he and the others can keep playing because they haven't turn off their consoles and have maintained a constant connection to Xbox Live since April 15. The band of 8 started out much larger, but numbers dwindled as consoles overheated and connections failed.
Although Campbell said that he and his fellow gamers are "not [playing] for competition, not for a prize, but for the love and memory of Halo 2," GamesRadar has graced the devoted bunch with access codes for the Halo: Reach beta. Microsoft's Stephen Toulouse even supported them in a tweet today: "To those noble folk keeping halo2 alive: we see you, and we salute you."
There's no telling how long the enduring individuals will remain online, but until the last one drops we figure it's worth showing our encouragement. Keep on keeping on, guys.